Using the minutely precipitation data of the Kunming national basic climate station from 1981 to 2014, the rainstrom formula fitted by Pearson Ⅲ distribution, Gumbell distribution, and exponential distribution are worked out respectively by the annual maximum value method. Tested by accuracy, based on the principles of minimum error，the formula fitted by the Gumbell distribution proved optimal. Contrasting the newly formulated formula with the five rainstorm intensity formula formulated respectively for Kunming and analyzing the spatial and temporal distribution features of rainstorm intensity in Kunming, the formula proved reasonable and applicable, which can provide the basis and reference for Kunming flood control engineering design and construction.